1. Field of the Invention
This invention relates to an optical axis correction device for correcting an optical axis within an optical spatial transmission device and more particularly to an optical axis correction device for correcting an optical axis by controlling a reflection angle of a mirror.
2. Description of the Related Art
In recent years, there has been vigorously performed to study a practical application of communication through a spatial transmission with light due to a lack of resources of electric wave or the fact that a troublesome procedure is required for installing a communication network of wireless system or wired system. However, it is an actual state that a device having a sufficient performance has not been provided yet in regard to an optical spatial transmission device over a long distance of several kilo-meters.
FIG. 12 illustrates a schematic configuration of an optical system segment of an optical spatial transmission device capable of performing an interactive optical communication. In this optical spatial transmission device, a beam of a semiconductor laser 31 modulated in response to a transmission signal is changed into a parallel beam by a lens 32 and is incident to a beam splitter 33. The incident beam is further incident to a concave lens 34 at an optical input/output side by a beam splitter 33, the beam expanded by the lens 34 is changed into a parallel beam by a lens 35 constituting a major lens segment together with the lens 34 and then outputted toward the optical spatial transmission device to be transmitted.
To the contrary, the beam received at the mating side is received by the lens 35. This beam passes through the beam splitter 33 after it is changed into a parallel beam by the lens 34 and then the beam is incident to the beam splitter 36. The beam splitter 36 divides the incident beam into a position sensing side and a receiving side. The beam divided to the position sensing side is collected by a lens 37 and is incident to the position sensing sensor 38. The position sensing sensor 38 detects a position of the incident light and transmits its detected signal to a control circuit (not shown). At the control circuit, an angle controlling operation to be described later is carried out in response to a sensing signal.
In turn, the beam divided into the receiving side is collected at the lens 39 and incident to the light receiving element 40. The light receiving element 40 converts the incident light into an electrical signal and sends it as a receiving signal to the receiving circuit. At the receiving circuit, the received signal is demodulated and recovered to its original data.
In this case, in order to perform an accurate beam transmission and receiving operation in such an optical system as above, it is always necessary to have an optical axis at the transmission side and an optical axis at the receiving side coincided to each other. However, the optical system is influenced by an external cause such as wind or the like, vibration generated within the device and further a variation in temperature or the like to cause the optical axes to be displaced from each other. In the case of a long distance communication, a minute displacement in optical axis may cause a certain trouble in communication, it becomes always necessary to correct an optical axis.
In view of the foregoing, there have been proposed various kinds of methods for correcting the optical axis.
FIG. 13 is a view for illustrating a first example of the prior art optical axis correcting device. An optical axis correcting device 50 has a barrel 51. Within the barrel 51 is integrally stored an optical system shown in FIG. 12. The barrel 51 is rotatably attached to an intermediate ring 52 by an X-axis receptor 54 around an X-axis. To the intermediate ring 52 is fixed an X-axis motor 53. Rotation of the X-axis motor 53 is transmitted to an X-axis receptor 54 through a driving gear 53a and a driven gear 54a. With such an arrangement as above, the barrel 51 is controlled in its rotation around the X-axis.
The intermediate ring 52 is attached to a base 55 by a Y-axis receptor 56 in such a way that it may be rotated around Y-axis. To the base 55 is fixed a Y-axis motor 57. Rotation of the Y-axis motor 57 is transmitted to a Y-axis receptor 56 through a driving gear 57a and a driven gear 56a. With such an arrangement as above, the barrel 51 is controlled in its rotation around the Y-axis. Rotation of the X-axis motor 53 and rotation of the Y-axis motor 57 are controlled in response to the sensing signal of the position sensing sensor 38 of the optical system shown in FIG. 12 in such a way that their optical axes may always be coincided to each other.
FIG. 14 is a view for showing a second example of the prior art optical axis correcting device. This optical axis correcting device is placed at the optical system shown in FIG. 12, wherein the same component elements as those shown in FIG. 12 are denoted by the same reference symbols to cause their description to be eliminated. Between the beam splitter 33 and the lens 34 are arranged an X-axis mirror 61, an X-axis motor 62 for controlling a rotation of the mirror, a Y-axis mirror 63 and a Y-axis motor 64 acting as a correction mechanism. The X-axis motor 62 and the Y-axis motor 64 are controlled in response to a sensing signal of the position sensing sensor 38, thereby angles of the X-axis mirror 61 and the Y-axis mirror 63 are controlled. With such an arrangement as above, an optical axis is corrected.
However, with the arrangement shown in FIG. 13, the entire barrel 51 is moved, so that its inertia mass is increased and a controlling response is inferior. In addition, as the bearing or the X-axis motor 53 and the Y-axis motor 57, it was required to provide component elements having a high accuracy and a high rigidity. Further, it was necessary to perform a correction of optical axis in a minute angle and it was required to provide a component having no back-lash in the motor or the like.
In addition, the configuration shown in FIG. 14 also required either mirror or motor, resulting in that their structures become complex and further it was required to provide a component element showing a high precision without having any back-lash.
In view of the above fact, the present applicant filed Japanese Patent Application No. Hei 10-014533 as an optical axis correction device for solving these problems.
FIG. 15 is a top plan view for showing a configuration of the optical axis correction device disclosed in Japanese Patent Application No. Hei 10-014533. The optical axis correction device 70 has a configuration in which a double-axis spring 71 is fixed to the upper surface of the frame 73 to be described later. The double-axis spring 71 is a thin disk-like member having a resiliency and it has concentric three rings 711, 712 and 713. The outer-most ring 711 is fixed to the frame 73. Between the outer ring 711 and an intermediate ring 712 is provided a clearance D11. The intermediate ring 712 is connected by Y-axis bridges 71a, 71b in such a state as one in which it can be twisted and rotated together with the outer ring 711. With such an arrangement as above, the intermediate ring 712 can be rotated around the Y-axis in respect to the outer ring 711.
Between the inner-most ring 713 and the intermediate ring 712 is provided a clearance D12. The inner ring 713 is connected to the intermediate ring 71 by the X-axis bridges 71c, 71d in such a way that it can be twisted and rotated. With such an arrangement as above, the intermediate ring 713 can be rotated around the X-axis in respect to the intermediate ring 712. In addition, a circular mirror 72 is fixed to the inner ring 713.
FIG. 16 is a sectional view taken along a line XII--XII of FIG. 15. As described above, the double-axis spring 71 is fixed to the upper surface of the frame 73. To the lower surface of the inner ring 713 is fixed a mirror holder 74. The mirror holder 74 holds a mirror 72. At this time, the mirror 72 is fixed in such a way that its reflection surface 72a is coincided with a central plane of plate thickness of the double-axis spring 71.
To the lower end surface of the frame 73 is fixed a base plate 75. Further, a base plate 77 is fixed through an annular spacer 76. On the base plate 75 are arranged every two X-axis driving mechanism 78X for rotating the mirror holder 74 around an X-axis and Y-axis driving mechanism 78Y for rotating the mirror holder 74 around a Y-axis, respectively. The X-axis driving mechanisms 78X and the Y-axis driving mechanisms 78Y are arranged at positions opposing against to each other over a crossing point between the X-axis and the Y-axis, i.e. an origin. However, in this case, one of the X-axis driving mechanisms 78X is placed at a reader's side in the figure, s o that it is not shown.
The Y-axis driving mechanism 78Y is a so-called moving magnet type voice coil motor and mainly this mechanism is comprised of a bobbin 78Ya fixed to the base plate 75, a coil 78Yb wound around the bobbin 78Ya, a yoke 78Yc fixed to the mirror holder 74 and a magnet 78Yd fixed inside the yoke 78Yc. Operation of the two Y-axis driving mechanisms 78Y is controlled at the optical axis correction device 70 so as to control a rotating angle around the Y-axis of the mirror holder 74.
Similarly, the X-axis driving mechanism 78X is also comprised of a bobbin 78Xa, a coil 78Xb, a yoke 78Xc, and a magnet (not shown), thereby a rotting angle around the X-axis of the mirror holder 74 is controlled.
On the base plate 75 are fixed a Y-axis angle sensor 79 and an X-axis angle sensor (not shown). The X-axis driving mechanism 78 and the Y-axis driving mechanism 78 are controlled at the optical axis correction device 70 in response to angle sensing signals attained from these Y-axis angle sensor 79 and the like and further controls an angle of a reflection surface 72a of the mirror 72. With such an arrangement as above, the optical axis is controlled for its correction.
In such an optical axis correction device 70, the reflection surface 72a of the mirror 72 is fixed in such a way that it may be coincided with a central plane of a plate thickness of the double-axis spring 71. Thus, even if the mirror 72 is rotated, its position in its Z-axis direction is not displaced.
In view of the foregoing, as a distance between the component parts of the optical system is changed in the optical spatial transmission device, a focal distance is changed, resulting in that a received light from the mating device, for example, does not make any focusing point at the light receiving plane of the position sensing sensor 38. As a result, the position of the optical axis of the received light from the mating device can not be detected accurately and an accurate optical axis correction can not be performed.
In view of the foregoing, the optical axis correction device 70 disclosed in Japanese Patent Application No. Hei 10-014533 was operated such that light beams across the optical axis correction device 70 in the optical system were made into parallel beams and even if the position of the reflection surface 72a of the mirror 72 was changed, no influence was applied to the focusing distance. In addition, as described above, the reflection surface 72a of the mirror 72 was fixed in such a way that it might be coincided with a central plane of plate thickness of the double-axis spring 71 so as to prevent the reflection surface 72a from being displaced toward a direction of Z-axis. With such an arrangement as above, since a distance between the lens 35 and each of the beam splitter 33, the position sensing sensor 38 and the light receiving element 40 and the like is not changed, it is possible to prevent a focusing point from being displaced and further an accurate correction can be carried out.
However, in the case that the received lights from the mating device passed through the lens 35 are changed into parallel beams before the optical axis correction device 70, it is necessary to make the received lights in parallel from each other through assembly adjustment of the lenses 34, 35. Even if an accurate assembly adjustment can be carried out, there is a possibility that characteristics of the lenses 34, 35 are changed in response to a variation in temperature and the received beams may not become in parallel from each other. For example, in the case that the device of which assembly adjustment was carried out at a room temperature of 20.degree. C. is installed at a site showing a surrounding atmosphere temperature of 40.degree. C., the lenses 34, 35 or the like are influenced by a variation in temperature, and the received lights are not made in parallel from each other before the optical axis correction device 70.
In turn, in the case that the reflection surface 72a of the mirror 72 was coincided with the central plane of the wall thickness of the double-axis spring 71, there was a problem that the heavy component elements such as the mirror holder 74 or yokes 78Xc, 78Yc or the like were concentrated below the center of rotation as apparent from FIG. 16, so that an inertia moment of the lower portion in respect to the rotating axes (X-axis, Y-axis) was increased and a responding speed of rotation of the mirror 72 in respect to the displacement of the optical axis was made inferior.